The present invention relates to nozzle flapper valves.
The nozzle flapper valve is a valve having a function of converting a minute mechanical variation to a large fluid pressure variation and provided with a nozzle a, a flapper b and a fixed throttle c arranged upstream of the nozzle as shown in FIG. 1 and is an oil pressure amplifying device of varying the nozzle back pressure Pn by varying the clearance .DELTA.X between the nozzle a and flapper b. In the nozzle flapper valve, by utilizing the principle that a fluid coming out of an oil pressure source kept under a fixed pressure Ps passes through the fixed throttle c and nozzle a and is discharged out into the atmosphere through the clearance .DELTA.X between the nozzle a and flapper b but, when the clearance .DELTA.X decreases, the resistance to the flow will increase and therefore the flow volume will decrease and, with it, the pressure drop at the fixed throttle c will also decrease and the pressure Pn at the output end d will increase, the output Pn is controlled by moving the flapper b to increase or decrease the clearance .DELTA.X between this flapper and nozzle a.
In such a conventional nozzle flapper valve, the flapper b is formed of a plate-shaped body, has the surface e arranged to be at right angles with the axis of the nozzle a and is intended to have the surface e always kept at right angles or substantially at right angles with the axis of the nozzle a even when the flapper is moved. Therefore, the moving mechanism for the flopper b in the conventional nozzle flapper valve is complicated, requires a very larger power when the valve is large and is hard to digitally control. Further, in such a conventional nozzle flapper valve, as the fluid jetted out of the nozzle a always hits the surface of one place of the flapper b, this place will be likely to wear and, when the valve is used for a long time with the clearance .DELTA.X between the nozzle a and flapper b made narrow, the clearance .DELTA.X will be likely to be clogged with the dust in the fluid so as to be substantially decreased.